The present invention relates to an information recording system with a high recording density and a thermally assisted recording system, in which a magnetic recording medium and a magnetic read/write head comprising a mechanism for heating the recording medium are provided.
As one of the information recording systems, a magnetic disk mounted in a computer or the like requires high recording density to support modern information overloaded society. In order to realize the high recording density of a magnetic disk system, it is desirable to narrow the distance between the magnetic disk and the magnetic head, to make the grain size consisting of the magnetic layer of the magnetic recording medium smaller, to increase the coercivity (anisotropy field) of the magnetic recording medium, and to enhance the speed of the signal processing technique.
In a magnetic recording medium, reducing the grain size leads to decreased noise but, on the other hand, a problem arises that the particles become thermally unstable. Therefore, the anisotropy energy should be made larger in order to be thermally stable with reducing the grain size. However, because of the limitation of the magnetic pole material used for the write head and the limitation of narrowing the distance between the magnetic disk and the magnetic head, it is difficult to increase the anisotropy field in proportion to achieve a high recording density in the future.
In order to solve the above-mentioned problems, a hybrid recording technique combining an optical recording technique with a magnetic recording technique has been proposed and is receiving attention. For example, in Intermag 2000 HA-04 and HA-06, the read/write head used is one on which a mechanism is added for heating the medium. While recording, the coercivity of the medium is reduced by heating the medium with applying magnetic fields. Because of this, it becomes easy to write on a medium with high coercivity, in which there was difficulty in recording using a conventional magnetic head due to insufficient magnetic field intensity. An MR (magneto-resistive) head is used for reproducing, which is a component of conventional magnetic recording system. The recording method described above is called thermally assisted magnetic recording.
Moreover, JP-A No. 344725/2001 discloses a perpendicular magnetic recording medium, in which a second recording medium having a perpendicular magnetic anisotropy and a greater intergrain magnetic exchange coupling is sputter-deposited on a first recording layer having the perpendicular magnetic anisotropy and a magnitude of the intergrain magnetic exchange coupling of almost zero. In JP-A No. 358616/2002, a magnetic recording medium is disclosed, in which a base layer including a magnetic layer, a switching layer including a non-ferromagnetic layer, and a recording layer containing ferromagnetic grains and non-ferromagnetic grain boundaries are formed in order on a substrate. A magnetic recording medium is disclosed in which the thickness of the switching layer and the distance between the magnetic grains constituting the recording layer are limited to satisfy the condition of TcB>Tsw, where the Curie point of the base layer is TcB and the temperature initiating the magnetic exchange coupling between the recording layer and the base layer is Tsw. In JP-A No. 79307/1998, a recording medium is disclosed, in which the Cr content is in the range of 21-24 at % at the grain boundaries of the microcrystalline grains constituting the magnetic thin film which becomes the magnetic recording medium.